The present invention relates to a method for observing the cross-sectional shape of a sample surface using a focussed ion beam apparatus, and more particularly relates to cross-sectional processing applied to observing grooves occurring with semiconductor elements and thin-film magnetic heads, etc.
Focussed ion beam apparatus are capable of processing and microscopically observing materials and in recent years have often been used in the processing and observation of the cross-section of samples, down to cross-sectional sizes for the most part from a few xcexcm to a few tens of xcexcm. In a basic procedure shown in FIG. 3A, first, locations of the sample which it is wished to subject to cross-sectional observation are specified (portions surrounded by a dashed line). However, it is necessary to open up the exposed part of the cross-section towards the front in order to monitor the cross-section. It is necessary to perform beam scanning from a severe angle with respect to the cross-section in order to obtain a microscopic image of the cross-section. When the processing regions are specified, the surface of the sample is subjected to rough processing using an ion beam from a vertical direction as shown in FIG. 3B. This processing is to open up a hole required for observation by causing the cross-section to be monitored to be exposed and therefore employs a large current beam to perform rough etching. This means that damage is incurred by the cross-section to be observed, as shown in FIG. 3B. When the hole-opening process finishes, polishing of the cross-section to be observed is carried out by etching with the beam current lowered, so as to expose the clean cross-section shown in FIG. 3C. A supporting table is then tilted and beam scanning is performed by irradiation with an ion beam from a severe angle with respect to the cross-section, and a scanning ion microscope image is obtained for the cross-section it is wished to observe.
However, an operation is carried out in advance to form a protective film on the material surface in order to prevent damage by the focused ion beam during processing. This operation is referred to as deposition. Typically, a protective layer is formed by spraying W(CO)6 or phenanthrene etc. onto the processing portions from a gas gun. However, when the material for the protective layer is the same as the material of the substance for the surface of the sample, a boundary of the original sample surface and the protective layer cannot be distinguished in an observed microscopic image. In particular, when the cross-sectional image to be observed is the surface shape of a groove, large amounts of protective film material are deposited at the groove so that the groove becomes buried and the original groove shape cannot be distinguished in a microscopic image.
In order to resolve the aforementioned problems with regards to technology for processing and observing cross-sections using a focused ion beam, the present invention sets out to provide a method for obtaining a microscopic image where the shape of an original material surface is clearly regardless of protective layer forming material becoming deposited at the surface of a sample when processing the cross-section.
The present invention achieves this object by first forming a covering layer of a different material to the material of a sample surface at the surface of the as-yet unprocessed sample. A protective layer is then formed by deposition and this portion is subjected to cross-section processing. A covering layer of a different material there exists at the boundary of the original sample surface and the protective layer deposited by deposition. The presence of the covering layer of a different substance in a microscopic image then enables the shape of the original sample surface to be clearly depicted.